CULTURE METHODS Culture methods employed depend on the purpose for which they are intended. The indications for culture are: To isolate bacteria in pure cultures. To demonstrate their properties. To obtain sufficient growth for the preparation of antigens and for other tests. For bacteriophage & bacteriocin susceptibility. To determine sensitivity to antibiotics. To estimate viable counts. Maintain stock cultures.

Culture methods include: Streak culture Lawn culture Stroke culture Stab culture Pour plate method Liquid culture Anaerobic culture methods

STREAK CULTURE Used for the isolation of bacteria in pure culture from clinical specimens. Platinum wire or Nichrome wire is used. One loopful of the specimen is transferred onto the surface of a well dried plate. Spread over a small area at the periphery. The inoculum is then distributed thinly over the plate by streaking it with a loop in a series of parallel lines in different segments of the plate. On incubation, separated colonies are obtained over the last series of streaks.

LAWN CULTURE Provides a uniform surface growth of the bacterium. Uses For bacteriophage typing. Antibiotic sensitivity testing. In the preparation of bacterial antigens and vaccines. Lawn cultures are prepared by flooding the surface of the plate with a liquid suspension of the bacterium.

Antibiotic sensitivity testing

Stroke culture is made in tubes containing agar slope / slant. Uses Provide a pure growth of bacterium for slide agglutination and other diagnostic tests.

Demonstration of gelatin liquefaction. STAB CULTURE Prepared by puncturing a suitable medium – gelatin or glucose agar with a long, straight, charged wire. Uses Demonstration of gelatin liquefaction. Oxygen requirements of the bacterium under study. Maintenance of stoke cultures.

Motility medium Gelatin liquefaction Oxidation – Fermentation medium

Agar medium is melted (15 ml) and cooled to 45oC. POUR PLATE CULTURE Agar medium is melted (15 ml) and cooled to 45oC. 1 ml of the inoculum is added to the molten agar. Mix well and pour to a sterile petri dish. Allow it to set. Incubate at 37oC, colonies will be distributed throughout the depth of the medium. Uses Gives an estimate of the viable bacterial count in a suspension. For the quantitative urine cultures.

LIQUID CULTURES Liquid cultures are inoculated by touching with a charged loop or by adding the inoculum with pipettes or syringes. Uses Blood culture Sterility tests Continuous culture methods Disadvantage It does not provide a pure culture from mixed inocula.

Blood culture bottles